A wing constituting an airframe of an aircraft is of a hollow construction, and a wing surface panel forming a wing surface is fixed to a structural member existing in the wing by a fastener member (fastener).
The fastener member fastens the wing to the structural member by inserting a pin-shaped fastener main body into through holes, which have been formed in both the wing and the member attached to the wing, from the outside of wing, and by fixing the front end portion of the fastener main body by using a fixture from the interior side of the wing.
The aircraft must make thoroughgoing provisions against lightning strikes. On a discontinuous surface between the wing surface panel and the fastener member or the like, dielectric breakdown tends to be caused by electric field concentration due to the presence of a structure end (an edge effect). When a leader that develops starting from a place of the dielectric breakdown and a leader that develops from a thundercloud combine, a lightning current of several hundred kiloamperes flows to the airframe.
Since a fuel tank is housed in the internal space of the wing, it is necessary to reliably suppress the production of arc discharge due to an electric current that flows into the tank via a fastener at the time of lightning strikes.
To meet such necessity, a structure has conventionally been proposed in which, as shown in FIG. 6, on the inside of a wing 1, a cap 6 is installed in a state of being separate from a fastener main body 4a of a fastener member 4, which penetrates a first member 2 corresponding to the wing surface panel and a second member 3 installed within the wing, and a fixture 4b, and an air-gap 7 filled with air is formed between the cap 6 and the fastener main body 4a, the fixture 4b (for example, refer to Patent Document 1).
However, the technique descried in Patent Document 1 does not provide a structure in which the cap 6 can be positioned with respect to the fastener member 4, and the installation position of the cap 6 depends on the worker. Therefore, the center of the cap 6 and the center of the fastener member 4 may be greatly misaligned. If, in the air-gap 7, a place where a gap between the fastener member 4 and the cap 6 is narrow is produced, the function (insulation properties) of the cap 6 decreases. In the worst case, if the cap 6 is installed in a state of being in contact with the fastener member 4, the function itself of the cap 6 may be impaired greatly. Therefore, it is necessary to perform management to prevent such impairment from occurring through the greatest care and guarantee of quality.
The cap 6 is installed on the second member 3 with an adhesive 9 as shown in FIG. 6A, or is outer-peripherally covered with a rubber (insulating material) 10 as shown in FIG. 6B. Therefore, in the installation site, the bonding work or the coating work of the rubber 10 is required, so that the work takes much time and labor. Needless to say, the interior of the wing 1 of the aircraft has a narrow space, and the above-described work performed at a secluded position provides very poor workability. Moreover, since the fastener members 4 are provided at several thousands to several tens of thousands of places throughout the wing 1, the deterioration in workability leads directly to the rise in cost.
Furthermore, the above-described work is what is called manual work, so that the work quality is easily varied depending on the worker, which also exerts an influence on the reliability. Therefore, management such as accrediting for these kinds of work (confirming through a practical test or the like that the worker has a specific technical level and giving authorization to the worker) is necessary.
Therefore, the inventors have already proposed the technique for the configuration in which an engaging section is formed in a portion of a fastener member projecting to the interior side of an airframe, an engaged section engaging with the engaging section of the fastener member is formed in the center of the inner circumferential surface of a cap, and the engaging section of the fastener member is engaged with the engaged section (see Patent Document 2).